<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #menu * {
            padding: 0;
            margin: 0;
            font: 12px georgia;
            list-style-type: none;
        }

        #menu {
            margin-top: 100px;
        }

        .dropdown {
            position: absolute;
            float: left;
        }

        #menu .dropdown .dropdown_item,
         .dropdown .dropdown_item,
         .dropdown:hover .dropdown .dropdown_item {
            display: none;
            list-style-type: none;
            width: 140px;
        }

        #menu:hover .dropdown_item,
        #menu:hover .dropdown:hover .dropdown_item,
        #menu:hover .dropdown:hover .dropdown:hover .dropdown_item {
            display: block;
        }

        #menu:hover .dropdown_item {
            position: absolute;
            font: 10px;
            bottom: 100%;
        }

        .button {
            display: block;
            width: 173px;
            height: 38px;
            padding: 0 10px;
            line-height: 38px;
            border: 1px solid #d8d7d9;
            border-radius: 4px;
            font-size: 16px;
            color: #333;
            background: #fff;
        }
    </style>
</head>

<body>
    <div id="menu">

        <div class="dropdown">
            <button class="button">点我</button>
            <div class="dropdown_item">
                <div>s12</div>
                <div>2vvv</div>

                <div>2vvv</div>
                <div>2vvv</div>
                <div>2vvv</div>
                <div>2vvv</div><div>2vvv</div>

            </div>
        </div>

    </div>
</body>

</html>